Metallic strip is formed into tubing by passing the strip through forming rolls which deform the strip into an open ellipse with the opposing transverse edges of the strip in close proximity. The strip then passes through a welding station which bonds the transverse edges forming a tube.
Subsequent to welding, the tube typically passes through at least one set of sizing rolls to transform the elliptical tube to a generally circular configuration. The means and apparatus for converting strip to welded tubing is disclosed in U.S. Pat. Nos. 3,700,158 to Schatz et al, 4,697,446 to Yamamoto et al and 4,905,885 to Hellman, Sr., all of which are incorporated in their entirety by reference herein.
It is desirable to enhance the inner wall of the tube by providing a textured surface to increase surface area. The increased surface area increases the transfer of the heat from a liquid flowing within the tube to an external heat sink. A variety of enhancement patterns are known to enhance the performance of a heat exchange tube. The patterns include corrugated ridges or diamonds as disclosed in U.S. Pat. No. 3,861,462 to McLain and pear shaped grooves as disclosed in U.S. Pat. No. 5,052,476 to Sukumoda et al both of which are incorporated in their entireties by reference herein.
One problem in the manufacture of welded tube is an extruded weld bead. Excess welding material flows from the weld and accumulates on the inner and outer walls of the tube. Removal of the bead generally involves removal of some base material. While the removal of base material is acceptable from nonenhanced (smooth) tube walls, removal from an enhanced surface results in damage to the enhancement pattern in the weld region.
One method to remove the weld bead, used primarily in the manufacture of steel tube, is disclosed in U.S. Pat. No. 2,352,306. An oxygen jet is directed against the weld bead soon after welding when the bead is still hot. The bead ignites resulting in a smooth weld seam. U.S. Pat. No. 4,905,885 discloses a hydraulically controlled bead reduction roller and a backing roller to flatten the weld bead. Another method is the insertion of an internal cutting tool.
When the inner wall of the tube is enhanced, the prior art methods of removing the weld bead are unsatisfactory. Mechanical flattening would damage the enhancement. A stream of oxygen would be deflected by the enhancements and inadequately ignite the weld bead. Cutting destroys a portion of the enhancement pattern.